The guilty ones

Jackman's sister-in-law Sarah disappears to London and throws herself into the river. What drove her to this? She was a woman with a seemingly happy homelife and two beloved sons. DI Jackman and DI Evans dig into Sarah's life. And Jackman realises he knew almost nothing about his sister-in-law's past. Then, they discover a woman in a neighbouring village died in similar circumstances. What is the connection to a convicted murderer whose family are convinced he is innocent? Who is really pulling the strings?